1. Field of the Invention
The present invention relates in general to latching covers or doors for access openings in bulk storage structures such as grain bins. In particular, the present invention relates to a latching cover of this type having increased ease of use.
2. Description of the Related Art
Bulk storage structures such as grain bins are typically large structures formed of overlapping panels of sheet material to form cylinders which are stacked one upon the other, as described and shown in U.S. Pat. No. 4,913,478 to Grossman. When the material stored within the structure is confined by the structure itself, such as with grain or other granular material, the cylindrical wall supports the material, causing large forces to be transferred through the walls in the form of hoop stresses.
As is recognized in the art, the formation of access openings in the sides of such structures reduces their structural integrity, and efforts have been made to allow covers for such openings to pass the hoop stresses therethrough. One method shown in the above-noted U.S. patent to Grossman and in U.S. Pat. No. 5,135,271 to Bestwick is to form a door frame having a rectangular periphery connected to the wall of the structure. Several covers are pivoted to one edge of the frame to allow the covers to move from open to closed positions. Each of the covers include a pivoted bar extending across the associated cover, with pivoting being between latched and unlatched positions. Each bar includes at it ends recesses which receive studs extending from the door frame, when the bars are in the latched position.
By this arrangement the bars may be lodged against the studs on the frame, allowing transmission of the hoop stress through the cover and/or latching mechanism. While these arrangements are adequate for transmission of the stresses, they are often difficult to use. For example, the forces exerted by the stored material often cause the bars to become lodged in the latched position, such that it is very difficult to move the bar to the unlatched position. Additionally, the latch arrangements require manual pressure to move to the latched position with the bars engaged. This pressure can sometime be high, increasing the possibility that latching will not be accomplished and the stress transfer arrangement not achieved.